Training apparatus



H. s. KNowmasI TRAINING APPARATUS Filed Maylz, 194s May l, 1945.

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TRAINING APPARATUS Filed'may 12, 1943 5 sheets-sheet 2 w filling ai i Mai l, 1945 l H. s. KNowLEs y `2,375,004 i l TRAINING APPARATUS Filed May 12, 1943 5 Sheets-Sheet 5 Ez/@22024.- fug/L j Know/e5 @y JMA W( MA g 6227i.

May 1, 1945.

H. s. KNowLE-s TRAINING APPARATUS 5 Sheets-Sheet 4 Filed May 12, 1943 May l, 1945- H. s. KNowLEs 2,375,004

TRAINING APPARATUS Filed May 12, 1943 5 Sheets-Sheet 5 l Aj Kink/65 @y im 4 combat, which methods and apparatus are adapt- 'actual target, or a motion picture'image oi' an` ent invention f oi simulating actual battle conditions as closely as automatic gun operation. The proper use oi' batldistractingl factors are add Viiiable for eco Patented May 1, 1945 v iiugh S. Knowles, River Josephine Knotts Kno Forest, Ill., assignor to'.V d

wles, River Forest,'Ill.

Application May 12, 1943, Serial No. 486,712

sa claims. (o1. ss-z) This invention relatesI to apparatus for training a person in the operation ot an automatic gun; More particularly, lt relates to methods `of and apparatus for producing sound and mechanical eii'ects simulating those encountered in war ed for use with gunner-y trainin duce an atmosphere of realism.

Gunnery training devices adapted to prov'de preliminary training in automatic gun operation areknown and consist, in general, of a gun which shoots a pellet by means of compressed air, which may be moved as Aan actual sun to aim nat the target, and which carries an actual gun sight. The target usually is ascale model of lan expected g devices to proactual target and its surroundingenvironment. In some training devices where a motion picture target is used, the. gundoes notshoot'a pellet. and the gun sight is simulated byv means of optcal eil'ects and means are provided for indicating the i accuracy oi' the aim. The apparatus o! the pres-V may be used with any of such traininsdevices.""'f Experience has demonstrated the desirability possible. This permits the segregation of trainees who possess the proper coordination, aptitudes and nervous andemctional stability required for tie effects in training'devices is highlyl effective for the conditioning oftrainees for Vthe unpar.

alleled ,noise of battle. Such "conditioning should .take place gradually. `The rnechanicsof gun manipulation .and aiming learned without the distr muzale'blast and general v'are preferably' first actionslof gun recoil, battle sounds. These V ed successively andincreased in'lntensity -1until their simulation of actual conditions is as close as is considered ad.-

nornic.. technological or traumatic ifmns.- I l The iiring of an actual gun is attended by a number of phenomena which cause degradation of muscular coordination and must be taken into consideration 'it simulation' approaching realism accomplished. 1) There is mechanism (2) There 'isasudden ilow` cr blast of air which compresses the thoraxand whips the clothing Aof the trainee. `Il'iave found that-the the recoil of the gun y airilow past the face and chest and compression There is an acoustic impulse of extreme intensity which causes pain in the ears of the trainee and is accompanied by a loud cracking noise.` The combination o1' (2) and (3) comprises the initial aerial shockimpulse caused by the gun discharge. It exhibits extrexnel:v high velocity and intensity,

and contains both mechanicalv and acoustical components. It is immediately followed by (4) a series oi impulses of lower intensity which produce a'boon'iinc noise. (5) There are echoes, which are the acoustic renections from nearby objects of the cracking and boomingnoises `'I'he echoes are sumciently common in actual nring positibns that they are considered to be a part oi typical gun sounds. They contribute a sense of nearby objects and, therefore, are a distracting factor. The trainee is usually incapable of determining the sequence with which the separate phenomena, except for the echoes, resister upon his senses. Mostsatisiactory results are obtained 'ii' they are made-to occur as nearly as possible in the order in which the actual phenomena occur.

To* `facilitate the description, the mechanical component oi' the initial'aerial shock' impulse will be called an air blast,` or air streaming. These .terms contemplate that now oi' air which-occurs on the detonation of an explosive. objectively,

air streaming manifests itself in translational movement oi' air and causes compression oi the thorax` and whipping o! the clothing. `Subjec-` tively, "air streaming" is characterizedby the sensation oi'4 air Allowing past the observer. This air streaming or .mechanical eiiectis aocomf l and suitable for conditioning trainees is to `be i the initial shock impulse and the acousti ing sound or impulse wave train;

of the'thorax are far more distracting than the panied by th e` acoustic crack or initial impulse.

'I'he acoustic or sound componente! the aerial shock impulse will be called an acousticv wave train. `'I'his includes the initial acousticvimpulse or sharp* cracker acoustic blast, the booming noise `or impulse wave train, and -the echoesA or echo wave train. The term initiaishock im`- pulse" will be `used to 'designatethe'combined eii'ects` oi"` air blast or air streaming and-the acoustic crack or initial acoustic impulse. The term "shock wave" will be employed to designate all oi the mechanical' and'acoustical eiiects except ior the echoes. That is, the` term inludes c oom- The use-of sound 'eireets `vinta" training` and amusementfdeviceaiis, ofcourse, not new. Previous apparatus have employed ordinary telephones or head phones, and low cr medium Dowered-.or horny typev speakers mounted at an aiipre-A viable distance from the listener. that'il. ata distance many times the diameter of the speaker diaphragm. Mechanical noise makers have also been used. All of such known devices have lacked realism and effectiveness for two or more of the following reasons: (1) none of them provided the sudden flow of air, or air streaming, past the listener or any appreciable compression of the thorax; (2) the initial shock impulse simulating gun blast did not have a sufiiciently steep wave i'ront orpossess sumcient intensity to exceed the pain threshold of many listeners; (3) the impulse wave train or booming noise did not resemble the actual wave train simulated, in intensity, rate of decay or general wave form; and (4) discrete echec'. ,vere not provided. The importance of these factors is discussed in further detail hereinafter.

The principal object of the invention is to provide methods. and apparatus for creating battle sounds having high distraction value which are synchronized with and complementary to the activities of and the visual action observed by the trainee.

A speeinc object is to provide apparatus for the artificial generation of shock waves simulating those created by the muzzle blast of the gun being fired, including the sudden flow of air which normally accompanies the actual shock wave.

Another object is the provision of means for generating echoes simulating the echoes which would occur in a typical environment.

Another object is to provide means for actuating the different effect-producing means in timed sequence.

Btill another object is the'provision of an emcient electroacoustic power conversion system which is capable of handling efilciently the high ratio of peak 4to average electrical power which is will become apparent from the disclosure con-- tained in the followingdescription.

Briefly, the invention consists in providing a pneumatic impulse generator which creates the air streaming upon the trainee and the sharp acoustic crack in faithful simulation of the similar phenomena produced by an automatic gun under actual firing conditions; It also provides a loud-speaker and suitable energizing means therefor, which provide acoustic impulses which faithfully simulate the booming noises and the echoes which are normally heard by the trainee in combat. Means are also provided for actuating in timed sequence, the pellet discharging mechanism of the model gun, a recoil mechanism for the model gun, the pneumatic impulse generator and theloud-speaker, whereby the diiferent effects occur in the normal sequence of occurrence of the actual phenomena being simulated.

The invention provides separate means for creating each of the various phenomena. This makes possible independent control of the intensity. quality and time sequence of the aerodynamic and acoustic contributions. lIt also makes possible the attainment of much higher electroacoustic conversion efficiency. In addition, the apparatus islight in weight andmay beoperated from a conventional convenience electrical outlet, whereby it is portable and easily installed.

,In the drawings:

l'ig. 1 is a time-pressure curve representing sir and acoustic pressure conditions accompanying the firing of an automatic gun;

Fig. 2 is an elevational view showing the general features of the training apparatus in a typical training environment;

Fig. 3 is a diagrammatic view showing a mechanism for actuating the different effects in timed sequence;

Fig. 4 is a fractional elevational view, partly in section, of a model gun, showing the means for discharging a pellet;

Fig. 5 is a fractional plan view of a similar gun showing a mechanism for producing recoil;

Fig. 6 is a sectional view of an apparatus for producing the air blast or air streaming;

Fig. l is a perspective view of one embodiment of a loud-speaker arrangement and a cabinet therefor;

Fig. 8 is a diagrammatic view of means for simulating part of the initial shock impulse, the impulse wave train and echo wave trains, and producing other battle effects;

Fig. 9 is a plan view, partly in, section, of the mechanical features of a portion of the wave train producing mechanism shown in Fig. 8;

Fig. 10 is a diagrammatic view of an a1ternative means for producing the initial shock impulse including the air streaming and acoustic crack;

Fig. 11 is a diagrammatic view of an alternative means for producing the impulse wave train. the echo wave trains and additional battle effects; and

Fig. l2 is a perspective view of an alternative arrangement of loud-speakers and the enclosing cabinet therefor.

In the drawings similar reference characters designate corresponding parts throughout. In Figure l, a time-pressure curve of a gun muzzle blast shock wave is shown. The curve shown in n solid lines is representative of the curves for the fili pressure registered by a piezoelectric pressure gauge 1% inch in diameter mounted at the gunners station and in a position normal to the front ofthe shock wave emanating from the muzzle of an actual small caliber automatic gun. In any specinc installation, the curve details depend upon the kind of gun used and acoustical environment which exists within several hundred feet of the gun. However, in substantially all cases the curves possess certain common characteristics. which will be discussed hereinafter, and if such characteristics are reproduced, the sound is readily recognized and satisfactory simulation is obtained.

The shock wave differs in one major respect from a purely acoustic wave. In the shock wave there is sudden compression of the air in the region of occurrence concurrently with rapid flow, or streaming, of the air from the compressed wave front to regions of lower pressure. This is the air streaming or air blast phenomenon mentioned heretofore. The translational movement of the air becomes negligible at a relatively short distance fromthe source of the shock wave. Part of the energy ofthe shock wave is converted into a compressional acoustic wave of the conventional type which travels a relatively long distance. The air particle 'displacement caused bythe acoustic wave is very small even in an extremely intense sound field. 'I'he time-pressure curve oi' 4Figure 1 is a measure of the combined aerodynamic pressure at the gunners position due to air streaming and the sound pressure as modiiied by the dynamic response of the pressurelauge. mthecaseofcertaingunsand crew .and gradually decay, as shown in Fig. 1.

positions. pressure impulses measured near the shock wave source in the manner speciiied heretoiore are characterized by a very rapid rise in incremental pressure, to a value of 15 pounds per square inch or more above atmospheric pressure. In typical gun crew positions, the muzzle blast pressure registered by the gauge, rises to a maximum in from 50 to 150 microseconds. Authorities assert that near the source the pressure rise at the shock wave front occurs in from 10-1" to 10"!x seconds. The greater time interval meas# `relative intensity of the `initial shock impulse as shown in dotted lines in `l'igure 1. The initial shock impulse `may thereby be made to exceed the pain threshold of most trainees and yet the balance of the wave train or boom portion may be kept below the pain threshold. From a Fourierintegral analysis of an isolated pulse, it can be shown that on a purely acoustic wave basis this abrupt pressure rise can occur only in the presence of very intense sounds in the supersonic and upper audible frequency ranges. It is this sudden intense pressure rise which causes much of the ear pain referred to heretofore. The high frequency components are rapidly attenuated `so the pressure rise is more gradual when measured at some distance from the source.

The initial air compression is followed by a rarefaction the character of which dependson the ground or primary .reflecting surface. The

impulse wave train which trails or follows the initial shock impulse is composed of a train of waves having both mechanical and acoustical components which oscillate about a mean value,

with a frequency which is not strictly constant, This wave train is identied by the ear as-a single sound. i

The echo wavetrain curves represent acoustic wavesreiiected from objects which are thirty feet or more from the source and which arrive at the f ear a sumcient time after the initial impulse to be identified as discrete echoes. For convenience in plotting, their amplitude has been increased in Fig. 1 by a factor of ten over the amplitude of the impulse wave train. The normal year is milliseconds or more to produce a separate sensation.

.'ll'ig. 2 illustrates aform of training apparatus 4in whichpellets are nredat model targets. It

will be obvious to anyone skilled- 1n the art that the invention may be used with a gun which does not nre a pellety and a target which is a motion Picture image projected upon a largefscreen or into a small box into which the trainee looks. The electropneumatic pelletfgun It is operated by the trainee ,II. Compressed air for firing the pellet is provided by the compressor il and is Areproduces a portion of the initial shock impulse conveyed to the gun Il by the air conduit It.

An electropneumatic pulse generator Il, which in this embodiment reproduces most of the initial shock impulse, is mounted -upon the supporting frame for the gun I0. Pulse generator Il is illustrated in detail in Fig. 6. The loudspeaker cabinet Il contains a loud-speaker whic and the impulse wave train, the echo wave trains and the recorded battle sounds. The cabinet it is mounted in a vertically adjustable' manner upon spaced upright supports il, which are mounted upon a control cabinet I8 which, in turn, is suported upon a wheeled carriage Il.

As shown more clearly in Fig. 7, the cabinet Il has hooks 2t which project rearwardly from the upper portions of the `sides thereof and engage pegs 2| which project from the supports I1 at different levels. The lower rearward edge of the cabinet rests against the forward surfaces of the uprights I1 to maintain the cabinet projecting forwardly in a generally horizontal direction. The cabinet I I contains loud-speaker 2l and vent pipe 24, speaker 23 being located directly above the trainees head and the diaphragm being arranged to direct the sound toward h im.

With this arrangement, the loud-speaker may be kept directly above and close to the trainee when he is firing in either the standing, seated or prone position. The directly overhead position is desirable because the sound in generated in the median plane through the lisiener's head and is localizedwith much more diillculty than sound generated at either side and is, therefore, more readily associated as coming from the intended object, as the gun muzzle or a diving model plane. In addition, when a large size cone speaker is selected to augment the streamingeffect as will be discussed hereinafter, movement ofthe trainee in `normal gun operation produces a minimum change in the loudness eect of the sound. .As the intensity at one ear increases, that at the other ear decreases. Such shift creates little or no impression on the trainee with the overhead arrangement.

The source of battle sounds and of control sisnals which may be employed, is preferably a phonograph of the conventional ilat record, film or magnetic tape type which is housed in control cabinet it. This cabinet also houses the phonograph amplifier, the sequence timing mechanism, the impulse wave train generator and the echo generator, thecontrol switches for making operatlve and inoperative the diiTerent distractive elements,` such as recoil, gun blast-and battle sounds, and the controls for'adjusting the intensity of such effects. Such apparatus will be described hereinafter.

In Flg.2 are also shown the airplanes 25 and 28 4which areisupported by trolleys 21 and II upon the overhead tracks 2l and Il, the supports for which are not shown, The airplanes are initially hidden from the view of the trainee by back drop Il. i The trolley 28 is held stationary by an electromagnetic release device comprising a pivotally supported arm 33 of electromagnetic material which engages a projection upon trolley 2l and holds `saldtrolley against the compression of a spring Il as shown in Fig. 2. The arm is held in the trolley engaging position by a compression spring Il. A solenoid Il is arranged in operative relation with a'rm 8l and upon the occui-rence of an electric impulse in input conductors 2 leading from a control device. which will be described hereinafter.eoleuoidll` draws down the adiacent end of arm 33 against the compression of spring 35 whereby the opposite end is raised and trolley 28 is released. Thereupon spring 34 gives the trolley 28 and airplane 28 an impetus toward the trainee. When the airplane 28 is returned by being pulled back to the release mechanism, it is pushed against the spring 84 until the arm 33 is again engaged by the trolley 28. A similar release 32 is provided in operative association with trolley 21 of airplane 25.

A model tank 31 is shown on track 38, emerging into the trainee's view from behind model house 38. The topographical scenery 4 0 provides a proper combination of moving and fixed targets. The tank 31 is propelled by a continuous chain (not shown) which follows the track 38 and is driven by suitable gearing 4I, which is driven by an electric motor 42. The operation of motor 42 is controlled by an electromagnetic relay 43 which operates switch 44 in the energy supply circuit. 45 for the motor. The arrangement is such that, upon being energized,'relay 43 closes the switch 44 against the tension of spring 48, and the tank 31 thereupon moves. The arrangement is such that the tank stops behind screening scenery for predetermined periods of time. The movement of the tank and the release of the airplanes is synchronized with appropriate battle sounds, and the mechanism for actuating such operations will be described hereinafter.

Pellet discharging mechanism While the mechanism for discharging the pellet from the model gun is not a part of the present invention, a suitable mechanism is shown `diagrammatically in Fig. 4. The model gun frame 41 carries handles 48 mounted thereon in a manner which will be described in connection with Fig. 5. Atrigger 48 is associated with one or both of the handles 48 and is adapted to operate a trigger switch for energizing the pellet discharging, recoil and gun sound mechanisms. The gun barrel 58 is mounted on frame 41 and contains a receptacle I for the pellet 82 at the rearward end thereof, and a magazine 53 from which pellets may be introduced singly into the receptacle 5I by the movement of sliding wall 54. Within receptacle 5I is a bowed leaf spring 55 which holds the pellet yieldingly in position. The wall of the barrel rearwardly of the pellet has an opening or port 58 therein which is in communication with an adjacent air chamber 51which is connected to air compressor I2 by means of air conduit 58. An electromagnetic core member 8i is arranged adjacent air chamber 51 and carries a valve member 82 which projects into air chamber 51 and normally closes port 58. Valve member 82 is normally held in the closed position by a compression spring member 83 which rests at its opposite end against bracket 84 which is mounted upon the frame 41. Valve member 82 is composed of electromagnetic material and is surrounded by a coil 85, which is connected to a suitable source of electrical energy by means of conductors 88. 'Ihe arrangement is such that upon the energization of the coil 85 the valve member is drawn back against the compression of spring 83 and opens port 58, admitting air under pressure to the pellet chamber 5I and discharging the pellet 52. Means are provided which are actuated upon pressing trigger 48 for energizing the coil 85 at predetermined times in synchronism with the remainder of the apparatus, as will be described hereinafter. Mechanism (not shown) is provided for withdrawing slide 54 to permit the next pellet to drop mu chamber u immediately after pellet sz is discharged.

Recoil mechanism A suitable mechanism for producing recoil in the model gun is illustrated in Fig. 5. This comprises handles 48 which are adapted to be grasped by the trainee, and upon one or both of which may be provided a trigger 48 which is adapted to operate a trigger switch as described heretofore. The handles 48 are mounted upon a recoil plate 12, which is mounted resiliently upon the members of gun frame 41 by means of bolts 14 which pass freely through openings in the frame members and the recoil plate. The recoil plate is arranged at the headed ends of the bolts. and is held in spring-floated relation to the frame by compression coil springs and 18 which telescope over the bolts 14. Springs 15 are arranged rearwardly of the frame members and between the frame members and the recoil plate and springs 18 are arranged forwardly of the frame members and between the frame members and the nuts 11 at the ends of the bolts opposite the headed ends. A solenoid core 88 is resiliently mounted upon recoil plate 12 by means of leaf springs 8| which are fastened at one end thereof to core 8|I and at the other end thereof to the coil plate 12. An electrical coil 82 is arranged within the core 88 and is connected to a suitable source of electrical energy by means of conductors 83. A movable armature member 84 is arranged within coil 82 and is normally held in a position partially forward of the coil by a tension spring member 88, which, in turn, is suitably supported by a bracket 88 which is mounted upon the core 88. Spring 85 is connected to a threaded rod member 81 which passes'through an opening in bracket 88 and is held in position by means of nuts 88, the

positions of which may be adjusted to control the tension on spring 85. Bracket 88 carries a stop member 88 which is adapted to stop the forward travel of the armature.

The arrangement is such that upon energization of the coil 82 the armature 84 is drawn rearwardly and strikes a blow upon the bottom leg of core 80, which blow is transmitted to the recoil plate 12 by springs 8| and thence to the handles 48 and to the hands and arms of the trainee. The force of the blow is made greater vand less by de creasing and increasing, respectively, the tension upon spring 85.

Pneumatic vpulse generator As explained heretofore, the element of air streaming is produced in the above embodiment primarily by the electropneumatic air pulse generator I4, which is mounted upon the frame structure of gun I8 as shown in Figs. 2, tand 5. The unit is shown in detail in Fig. 6 and consists of a horn member 8| which may be composed of metal or other suitable material and is of generally elongated oval shape in transverse section and oi' considerably greater width than height to present a horizontally elongated mouth. The horn mouth is directed upwardly and rearwardly and projects through an opening in the gun frame, the walls of the horn resting against the frame to hold it in position as shown in Fig. 4. The horn is closed at its throat and has V-shaped ports 82 in its upper and lower walls adjacent the closed end of the throat. The horn is mounted upon a plate member 83 which encircles the throat portion and in turn is fastened to a bracket member 84. A dome-shaped member 88 is mounted ngure, upon `energizatlon of the amature.

plate 99 and encloses the throat portion of the `horn and forms an air chamber 96 surrounding such throat portion. I'he wall of dome-shaped member 95 has a threaded opening therein into which the nipple 91 is threaded. Conduit 98, leading fromthe air compressor I2, is connected to nipple 91 and serves as a supply of air under pressure. An open-sided generally U-shaped, balanced-pressure valve member 99 is arranged in exterior telescoping relation with the upper and lower walls oi.' the valved throat portion of the horn. Valve member 99 has ports |00 therein adapted to cooperate with the ports 92 of the horn. Valve member 99 is preferably composed of a lightweight material, such as a light metal alloy, and the ports are V-shaped, the orientation of the V being the reverse of that of the ports 92.0f the horn, whereby when the ports 92 and I00` are in register with each other an extremely rapid flow of air takes place therethrough. The rearward end of valve member 99 is connected to stem |0| and is adapted to be operated thereby. Stem |0| is alsopreferably composed of a lightweight material and passes through a substantially central `opening |02 in dome-shaped member 95. The opening is sealed by a compliant sealing gland |03, which may be composed of rubber, and which is held in place by gland nut |00.

The projecting end of stemv |0| is threaded and is connected to a vibrating strip member |05, the two being held together in relatively adjustable relation by threaded nuts |06. An angle member |01 is fastened to strip |05, and armature member |00, which may be composed of a stack of electromagnetic metal laminations, ls'fastened to angle member |01 by rivets |09. A generally U- shaped core ||0, which may also be composed of a stack of velectromagnetic metal laminations, is mounted upon a supporting member |I| which is fastened to bracket member 94, the core ||0 being arranged with the ends of the U in spaced adjacent relation to the ends of the armature |09. A coil ||2 is mounted upon the core ||0 and the terminals ||3 of the coil are suitably connected inch, is introduced into the air chamber 99 and `the coil; ||2 ismomentarily connected to the source of electrical energy by means which will be described hereinafter, which causes an impulse to be imparted to armature |09, such impulse being transmittedby strip |00 and stem 0| to l valve'member 99. The mass of the moving system,

the character of-the electrical pulse and the stiflness of strip Ill determine the abruptness with which the valve opens. High stiffness and a.l steep wave front electrical pulse are `desirable for a very abrupt opening. The compliant sealing gland |09 serves as a damping member to damp the free oscillations of the vibrating system.

Rearward motion of valve member 99 brings the ports |00 thereof into register with the ports 92 of the horn fora short interval during each opez'-, atingVcycleLand at such interval a slug of air under high pressure is ejected from the mouth of the horn. The valve member 99 is shown in Fig. 9 with the ports out of register. The recipincreased width of the horn insures that the air blast `will be distributed adequately throughout the sphere of action of the trainee. A succession of the electrical impulses is delivered to the coil I2 such that properly timed air pulses of the desired duration are emitted by the horn.

The pneumatic pulse generator may supply the y steep initial portion of the wave in Figure 1 as Well as the balance of the initial positive pressure pulse. This necessitates a very abrupt`opening of the pulse generator valve. To achieve this the current wave of the electrical impulse lfed through rocating parts move to the right, as viewed in thisV4 the coil ||2 must have a very steep wave front. To accomplish this, the coil is constructed in such manner that its inductance is low, its resistance is moderately high and a condenser, such as condenser IH is connected in series with the `coil input as shown in Fig. 4 `or any other circuit which discriminates against low frequencies, as for example, a high pass filter similar to the network 25I, which will be described hereinafter in connection with Fig. 10, may be connected in the coil input. In such an arrangement, the amplitude of the electrical impulse is very high.

, In the described pulse generator, streaming occurs when the valve is open which is normally for only a few milliseconds. The exact time depends yon the shockwave which is to be reproduced. The air pressure is greater than atmospheric. The V-shaped, or flared ports 92 and |00, permit the rapid flow of air necessary for the blast effect. Acoustic radiation in the ordinary sense ispresent to but a slight extent. However, if the valve opening is very rapid and abrupt a steep initial wave front is produced which causes the cracking sound mentioned above and causes appreciable amounts of high frequency acoustic energy to be radiated. The streaming effect, nevertheless, greatly predominates.

It is desirable to exceed the pain threshold at least slightly in training. Very little is known of the pain threshold of the human ear because in vestigators have wished to avoid ear trauma. Most authors have reported that it lies in the vicinity of 600 dynes per square centimeter in the middle audio frequency range. I have found that pressures of not less than 2000 dynes are required for most trainees. From 5000 tp 10,000 dynes per square centimeter are necessary for some. The described apparatus is designed to give the mentioned pressures, and means are provided for adjusting the intensity for diierent trainees comprising the adjustable pressure reducing valve ||5 in the air supply conduit 99.

A relatively minor part of the initial shock impulse and a major part of the impulse wave train, together with the echo wave train, is provided by the overhead loud-speaker 23. `This speaker `is preferably of the moving coil type having a high emciency and force factor and having a voice coil capable of dlssipating appreciable heat. The cone should have `a diameter of not less ,than` ten inches and preferably from l5 to 18 inches. whereby it is adapted to contribute to the streaming effect.

v 'Appreciable streaming and augmented acoustic radiation at the fundamental firing rate of the gun are provided by the cabinet lli itself when the latter is properly designed so as to function as a Helmholtz resonator with pipe 24 serving as` the open neck thereof. The cabinet is a complete enclosure except for the pipe 24. The speaker diaphragm opening is closed by the speaker diaphragm. The net internal volume V of the interior of the cabinet Il, `the length L ofthe pipe 24 and the cross sectional area A ofthe pipe 24 are related .in a manner represented by the equation:

c l A fw'v (l) where f is the resonant frequency of the enclo sure and pipe with the loud-speaker cone held motionless, and c is the velocity of sound in air. Approximate values for f are 10 per second for a 50 caliber machine gun and 20 per second for a 30 caliber machine gun. The diaphragm opening may be covered by a protective screen 22 and the interior end of pipe 24 may be covered by a porous fabric I8 to control the damping of the resonator.

Wave train generator An electrical system for generating a. minor portion of the initial shock impulse and a major portion of the impulse wave and echo wave trains is shown diagrammatically in Fig. 8. This arrangement is contained in cabinet I2 and consists in input conductors and |2| one of which has an electrical make and break mechanism 2|| (Fig. 3) connected therein which will be described hereinafter, whereby said conductors are adapted to deliver timed electrical impulses to the circuit associated therewith. Conductor |20 has a condenser |23 connected in series therewith which is shunted by a resistor |24. Conductors |20 and |2| are connected to the input of an electromechanical motor |28 which may be the electromechanical unit of a moving coil loud-speaker and is adapted to convert electrical impulses into me-y chanical impulses. The output of electromechanical motor |28 is connected to one end of a mechanical transmission line |21 and is adapted to deliver mechanical impulses to said transmission line. The transmission line |21, which will be described in detail in connection with Fig. 9, comprises a resilient coil spring mechanism which sustains each mechanical impulse as a series of vibrations having the natural periodicities, or 'frequencies. of the transmission line. The transmission line contains one or more damping members |28, which introduce a damping effect whereby the sustained vibrations diminish in energy and cease according to desired characteristics which simulate the characteristics of the impulse wave train shown in Fig. 1.

'I'he output of mecahnical transmission line |21 is connected to the input of an electromechanical generator |29. which is illustrated as being a piezoelectric crystal unit and is adapted to convert the mechanical impulses into electrical impulses. The output of electromechanical generator |20 is connected by conductors |30 to one input of a multiple input amplifier i3 the output of which is connected to the input of a loudspeaker 23 by conductors |32. The output of electromechanical motor |28 is also connected to one end of a second resilient spring transmission line |50, which will also be described hereinafter, and which is relatively long withrespect to transmission line |21 and extends in the opposite direction from transmission line |21 and is supported at an intermediate portion and at its opposite end by flexible supports |82 and |83.

In operation. an electrical impulse is applied to conductors |20 and |2| as described heretofore and is transmitted to the input of electromechanical motor |28. The steepness of the wave front of the impulse is increased by condenser- |23. The electrical impulse is converted by motor |28 into a mechanical impulse, which is delivered 'to tains the impulse as a series of damped vibrations. The train of vibrations, delayed by a small time interval, is delivered to the electromechanical generator l25, which reconverts the mechan ical vibrations into electrical vibrations which are transmitted through amplifier |3| to loudspeaker 23. The impulses transmitted directly through line |21 are delivered relatively quickly to the loud-speaker and the resulting acoustical output of the loud-speaker constitutes the impulse wave train similar to that shown in Fig. 1.

'I'he mechanical impulse of motor |25 is also delivered to mechanical transmission line |50 and the resulting train of vibrations set up in said transmission line travel from the motor |25 to the opposite end of said transmission line and are there reflected and return tothe motor |20 where they are delivered to the short transmission line |21 and are transmitted thereby to electromechanical generator |20 and thence to amplifier |3| and loud-speaker 2l. Said second train of impulses arrive at loud-speaker 23 after the impulse wave train heretofore described, and simulate the echo wave trains shown in F1a. l.

- The mechanical features of the means for pro- '.ducing the wave trains, comprising electrothe vibratory transmission line |21, which susmechanical transducers |25 and |23 and transmission lines |21 and |00, are shown in Fig. 9. They consist of a supporting base |45 upon which is mounted the motor |28, consisting of a loudspeaker moving coll mechanism' which comprises a bracket |48 which is mounted upon the base |45 and carries the two annular end plates |41 and |48 of magnetic material, arranged generally transversely of base |45I the outer hollow cylindrical permanent magnet |55 and the inner hollow cylindrical member |5| of magnetic material, said cylindrical members having their axes extending generally longitudinally of said base. 'I'he arrangement is such that an annular air gap |52 is provided surrounding one end of the inner cylindrical member |5| and between said member and annular member |41. Within air gap |52 is located the voice coil |53, which is wound upon cylindrical bobbin |54 of elec trically non-conductive material and has terminal conductors |20 and |2| connected thereto. which are the same conductors |20 and |2| as are shown in Fig. 8. One end of the bobbin |54 projects beyond air gap- |52 andis attached to a flexible annular membrane |58 which extends outwardly from the bobbin and is supported adjacent its outer periphery upon an annular ring member |51 which, in turn. is mounted upon an edge portion of the annular core member |41. Membrane |58 may contain annular corrugations as shown and may be composed of an air-pervious fabric stiftened sufficiently to maintain its corrugated shape as by being lightly impregnated with a resin in a manner to avoid illling the pores oi the fabric. The exibility of such a fabric in response to the impulses of the moving coil |52 is substantially as great as that of a similar fabric unimpregnated with resin. Conductors |20 and 2| may be cemented to the surface of membrane |58. A conical member |55 of rigid nonmagnetic material internally bridges the same end of bobbin |54 and is fastened thereto.

The relatively long coil spring member |55 is attached at one end thereof to said bridsln member |58 and extends generally longitudinally of the base |45 and may pass through the hol` low interior of the inner cylindrical core member |5| and is attached at the other end thereof to the central opening of a corrugated porous ,fabric membrane |62, which may be similar to membrane |66 and is supported at its periphery upon bracket |6| which is mounted upon base |46. Spring |66 ispreferably in an unstressed condition, that is, under neither tension nor compression. A support for the intermediate portion of spring |66 is provided by a second corrugated membrane |66 which is supported at its periphery upon a bracket |64 which is mounted upon base |46. Spring |66 passes through a central opening in said membrane |63 and is attached to said membrane.` Membranes |62 and |66 are preferably readily responsive to the vibratory motion of spring |66.

The c oil spring |21, which is preferably maintained in the unstressed condition, is also fastened at one` end thereof to bridging member |66 andextends in a direction opposite from spring |66 and is fastened at the other end thereof to the driving member |65 of the electromechanical generator |26 which may be a piezoelectric crystal unit, as described heretofore. 'I'he driving'member |66 is clamped upon the endsof the two juxtaposed crystal laminae |61, the opposite ends of which are clamped between the arms |66 and |66 of a supporting bracket |1| v which is mounted upon base |46. A cushioning .member |12 is interposed between Vthe laminae and the arms |66 and |66 and a similar member |16 is inserted between the laminae and driving member |65. The exterior surfaces of the laminae |61 are connected to one of the conductors |66 and the surfaces which are in contact with each other are connected to the other conductor |66 in accordance with accepted practice.

Damping and pulse reflecting members |26 are fastened to spring 2,1 at points which are spaced apart and spaced from the ends of the spring.` Damping members |26 also support the intermediate portions of the spring, and are composed of masses |66 of a material having suitable weight, such as metal, and are mounted upon the ends of arms |6| which are fastened to bracket member |62 which is mounted upon base |46.

To further modify the damping effect in the ,desired manner, members' |63, which may be composed of a non-vibratile material, such as leather, cork, rubber, felt or other fibrous construction, or the like, may be attached to the arms |6| as by sluins together the surfaces thereof.

i `In operation, the momentary electrical impulse applied to the conductors |26 and |2| is conveyed lto the moving coil |66. The coil, being in the field ofmagnet composed of members' |41, |46, |66 and |6|, undergoes a mechanical impulse in responseto the electrical impulse, which impulse The same initial mechanical impulseundergone by the moving coil |66 in response to the electrical impulse is transmitted to the relatively long coil spring |66 and sets up a train of vibrations in the springv |66. Such vibrations travel to the opposite end of the spring and are there reflected and returnto the bridging member |66. where they are delivered to the end of spring |21 and are transmitted by said spring to electromechanical generator 26 and are thence conveyed as electrical vibrations to loud-speaker 26. There is a time lag between the delivery4 of the initial impulse and that of the reflected impulse i to spring |21. The construction of spring |66 is such that the sound emitted by loud-speaker 26 in response to said reflected wave train is similar to the echo wave train illustrated in Fis. l. v

A coil spring such as the springs contained `in i transmission lines |21 and |66 is a compliance member having distributed mass, and exhibits an infinite number of resonant frequencies. The

istransmitted via bobbin |64 and bridging memter lss to spring |21. A trein or vibrations is set upin the spring |21 in response to said impulse. because of the natural Avibratile character of the spring, and the initial impulse and wave train are delivered by the spring to the driving member |66 of the electromechanical generator |26. 'I'he mechanical wave train is converted into an electrical wave train by generator |26,` `and is delivered thereby to conductors |66 `and is thenceconveyed to amplifier 6| and loudspeaker 26. Damping members |26, in addition to damping the vibrations, partially reect them and `by suitably locating the damping'members and choosing the characteristics of the spring |21 and theV damping `members |26, a wave train similar tothe impulse wavetrain illustrated in Fig. 1 is obtained in the loud-speaker output.

spaced masses |26 act as damping and reflecting members and, in effect, with respect to the low and middle audio frequency range.' provide in the transmission line |21 an alternating succession of lumped compliancesand masses. f

Time-sequence mechanism |66 drives a cam member |66, the cam surfaces of which cooperate with cam follower |61. Cam follower |61 is pivotally mounted at its other end upon a stationary support |66 and is urged with vspring pressure against the cam surfaces. Cam

follower |61 carries one member of a pair'of cooperating contacts |66, which contacts are held separated when the raised surfaces of cam |66 engage the cam follower` |61 and are in `contact with each other when the cam follower engages the depressed surfaces of the cam. One of the contacts |66 is connected by conductor 26| to the conductor 262 which, in turn, is connected to conductor |6| leading to the source of energy, while the other contact is `connected to the conductor 66 which leads to the solenoid 66 of the pellet discharging mechanism. The second conductor 66 leading from the pellet discharging fmechanisxn is connected to the second conductor |62 leading to the source of electrical energy. A switch 266, whichis adapted to be operated by the trigger 46 shown in Figs. 4 and 5; is inserted in the supply conductor 262. 'l i i 'I'he gears |64 and |66 are provided to furnish the desired speed ratio between `.shaft |66 and cam |66, but itis understood that these gears may be omitted if desired and the cam mounted directly upon the shaft |66. In usual practice. a pellet is discharged only a fraction of the number o! times that 4the gun ring operation is simulated since the visible pellets correspond to tracer projectiles.

A second cam 266 is mounted upon shaft |66 and cooperates in a manner similar to that described heretofore with a camfollower 266' to l engage and 2t? which, in the engaged position, connect conductor 202 leading from the source of power to conductor t3 leading to the recoil producing mechanism shown in 5. The second conductor 02 leading to the recoil producing mechanism is connected to energizing conductor E92.'

In a similar manner, cam 208 is also mounted upon shaft |93 and cooperates with a cam follower 209 which engages and disengages contacts 2|0 which, in the engaged position, connect energizing conductor. 202 to conductor ||2 leading to the solenoid of the pneumatic pulse generator shown in Fig. 6, and cam 2|| is mounted upon shaft |92 and cooperates with cam follower 2|2 which causes the engagement and disengagement of contacts 2|2, which, in the engaged position,

, connect energizing conductor 202 to conductor |20 leading to the input of the loud-speaker system shown in Fig. 1l. The second conductors ||2 and |2| leading to the pulse generator and the loud-speaker system, respectively, are connected to the second energizing conductor |92. Switches 2N, 2|5, 2|6 and 2li are arranged in conductors 66, 83, H3 and irl whereby the different effect-producing mechanisms may be rendered inoperative if desired.

Cams |96, 205, 208 and 2|| are arranged to close the respective circuits associated therewith at `such times as to actuate the different elements of the apparatus in the desired time sequence. If desired, speed-changing gears, such as gears |92 and |95 may be interposed between shaft |92 and any of the cams to produce any desired ratio of rotation thereof, and -the shapes of the cams may, likewise, be modified to produce a number of contacting operations during a single revolution. With the shaft |93 turning in the direction indicated by the arrow in Fig. 3, and the cams arranged as there shown, the elements will be actuated in the following order: first, the pellet discharging mechanism; second, or al; substantially the same time, the electromechanical motor; third, the recoil producing mechanism, and fourth, the pulse generatorl I4. In actual gun fire, the impulse wave train, simulated by loudspeaker 22, follows the air streaming and sharp cracking sound, simulated by the pneumatic pulse generator. In the present apparatus, actuation of the wave train mechanism is advanced with respect to actuation of the initial shock impulse producing means because of the time delay incident to the operation of the wave train mechanism as described heretofore. The order of actuation may be varied as desired. 'I'he closure times for the various contactors may be determined by aural observation, and they may also be determined by means of an oscilloscope connected to the high pressure electroacoustic gauge mentioned heretofore.

As stated heretofore, conductors |9| and |92 are connected preferably to a source of alternating current energy. This may be the common 60 cycle 110 volt service supply whereby an ordinary convenience plug and outlet arrangement may be used. The contactors are arranged in such manner that they close each circuit upon the occurrence of a voltage peak and preferably open it upon the occurrence of a current null.

The duration of each contact is very short. In a specific application where a 50 caliber machine gun was being simulated the following times were used; approximately 20 milliseconds for the pellet discharging mechanism, 50 milliseconds for the recoil mechanism, and from 4 to 12 milliseconds for the pneumatic pulse generator and the loud-speaker. The use of a synchronous motor, as described heretofore, makes it possible to arrange the closingand opening of the circuits at the desired times in the voltage and current cycles. If desired, however, a direct current energy supply source may be used.

of which is conveyed by conductors 226 to a sec ond input circuit of amplifier |3| and thence to loud-speaker 23. The multiple input amplifier |3| may be constructed according to known practice to provide independently the desired gain and tone qualities with respect to the energy -delivered to it from the phonograph pickup 225 and4 the desired gain and modification of the wave trains received by it from the electromechanical generator |29.

The record 224 carries inscribed thereon battle sounds, such as the sounds of near and distant guns, moving and ricocheting projectiles, human cries, the roar and clatter of mechanized equipment, etc. It also carries a plurality of signals, each of which may be characterized by a different frequency, or band of frequencies, which signals are spaced apart in time sequence. Such signals are picked up by pickup 225 and electric signals of corresponding frequencies are thereby impressed upon conductors 226, amplifier itl and conductors |22. A plurality of electric wave filters 230, 23| and 232 are connected in parallel relationship with veach other to conductors |32 by means of conductors 222, 224 and 225. Each of said wave filters is constructed in accordance with well known practice to transmit electric energy upon receiving in the input thereof energy of a particular frequency, i. e. it is a pass filter with respect to such frequency. For example, filter 230, upon receiving a signal of a particular frequency in the input thereof delivers an electric impulse to the output conductors 226 thereof which impulse is converted -into pulsating direct current by means of rectifier 231. Said impulse is conveyed to electromagnetic release 22 by said conductors 226, thereby effecting the release of airplane 26.

In the same way, wave filters 22| and 222 are adapted to deliver electric impulses to conductors 238 and 240 to effect the release of airplane 26 and the operation of tank 21.

Operation `42, whereupon tank 2l emerges into the View of thegunnerll. Heaimsthegunllatthctaak record 224. The gunner aims the gun at the airplane and presses the trigger. In this way the operations continue under conditionsv closely simulating battle conditions.

Alternative air .streaming` and wave train` apparatus An alternative apparatus for producing the air streaming, the initial sharp cracking noise, the impulse wave train and `theecho wave trains is shown diagrammatically in Figs. and 11. The

1 apparatus for producing the initial air streaming and sharp cracking sound or mosto! the initial lshock impulse is shown in Fig.'10. This consistsof a shock impulse loud-speaker 250 which takes the place of the pneumatic pulse generator I4 shown in Figs. 4 and 6. The loud-speaker may be of the moving coil type and is connected to input conductors ||3 through a network 25|, which is so constructed as to modify the character of the incoming electrical impulse so as to increase the steepness of the wave front. The

network 25| consists of a transformer having the primary 252 connected to input conductors ||3 and an adjustable secondary 253. Output con` ductors 255 and 254 are connected across the secondary 253 and are connected to the input of the loud-speaker 250. Capacitors 256 and 251 are connected in series with output conductor 255 and resistors 258 and 259 are connected, respectively, in shunt relationship with capacitors 256 and 251. A reactor 26|) is connected across conductors 254 and 255 at a point in conductor 255 between capacitors 256 and 251. instable secondary 253 provides a secondary potential of a value to produce the desired intensity of impulse in the loud-speaker 250, and the combination of thevtwo resistors and the two capacitors and reactor 260 comprise a high pass filter having a cut-off frequency above the irequencyi of the power source and possessing a characteristic impedance approximating the impedance of the loud-speaker 250 at the lter cuton frequency. The diaphragm assembly of the speaker is so chosen and the resistorsare of such a value that there is negligible energy stored in the reactive elements of the mechanical or electrical parts of the system at the time each successive impulse is applied to the network. The values of the capacitors and the reactor are determined by ordinary filter theory in accordance with the impedance of the voice coil ci the loudspeaker and the desired cut-ofi frequency. In a specificinstance, the capacitance of each con- The ad-` The output of the loud-speaker possesses characteristics similar to those of the iirst positive impulse shown in dotted lines in Fig. 1. which occurs in the first 150 microseconds and makes an appreciable contribution to the remainder of the wave train.

In this embodiment, the remainder `of the-impulse wave train and the echo wave trains are generated by the apparatus illustrated in Fig. 11. 'I'he input conductors |20 and `|2| leading from the make and break apparatus (see Fig. 3) and containing condenser 210`an'd bridging resistance 21| therein, are connected to the input of an electromechanical transducer 2,12 which may be similar to the electromechanical motor |25 shown` in Figs. 8v and 9.' Vibratory coil spring transf mission lines similar to those shown in Fig. 8 are associated with the electromechanical transducer 212. Thecorresponding'parts in Figs; 8 and 11 areindicated by the same numerals.' The vibratory transmission line |21 extends in one direction fromthe output member of the transducer and is fastened `at the opposite end thereof to a support 214, which maybe the piezoelectric crystal unit |29, the output leads |30 of which may be disconnected from any load device, whereby the crystal unitserves only as a support for the end of the line |21. The other transmission line |60 extends in the opposite direction from said output member and is supported at spaced locations by membranes |52 and |03. Output conductors 215 are also connected to the conductors 20 and |2| leading to themoving coil of transducer 212, conductors 215 being connected to the first input of the multiple input amplifier |3|, which is similarto the multiple input ampliiier |3| of Fig. 8 and which has associated with the second input thereof the same phonograph battle sound and signal creating mechanism and with the output thereof the same wave filters and loud-speaker as has been described in connection with Fig. 8, the similar parts being designated by the same numeralsl In operation, an electrical impulse is received by conductors |20 and |2| and conveyed to the electromechanical transducer 212, which is simdenser was of the order of 16 microfarads where the voice coil impedance was 6 ohms.

In operation. the electric impulse is conveyed directly from the inputlconductors through the network to the loud-speaker. Because of the short duration oi the impulse, instantaneous elec- 4tric input energy values up to 3.000 volt amperes may be applied to the voice coil `of a speaker having a maximum rating of 40 volt amperes.

lar to transducer |26 in Figs. 8 and 9 and delivers a correspondingmechanical impulse to the transmissionlines |21 and |60. A train of vibrations is set up in line |21 and is transmitted to the end of the line, where it is reflected, some components also being reflected from the damping members |28, the reflected train being delivered to the moving coil |53 and a correpsonding train of electrical impulses being set up in said coil, which train is delivered to conductors |20 and |2| and thence to conductors 215 leading to the input ofamplifier |3i, Said train simulates the :impulse wave train shownin Fig- 1. A train of mechanical impulses similarly set up in transmission line is reflected from the end of said line back through the line andto the moving coil |53 (Fig. 9) whereby it is converted into an electrical wave train which is alsotransmitted to the input of amplifier |3|.

Fig. 1. The wave train output of amplifier |I| is conveyed to loud-speaker 23. i

Both the initial and echo electrical wavetrains 4 The latter wave train simulates the echo wave trains shown in sorbed by moving coil |53 is converted into mechanical energy to provide the mechanical pulse in the transmission lines |21 and |60. Some of the mechanical energy is dissipated in the transmission lines and in the damping and support members which produce the desired multiple rei'lections of the mechanical pulse. Of the mechanicai pulse energy absorbed from the lines by coil |53 only a fraction is reconverted into electrical energy. The gain or amplification of amplifier |3| from terminals 215 is made such that the ampliiled impulse wave train energy applied to speaker 23 lrepresents half or more of the output capability of the amplifier. When the peak input to the shock impulse speaker 25|) is 3,000 volt amperes the peak wave train power delivered by the amplifier |3| to loud speaker 23 need be only of the order of 50 volt amperes, assuming that speakers 23 and 250 have equal efiiciencies. This indicates the marked reduction in amplifier power handling capacity obtained by providing the separate heretofore described means of obtaining the initial shock impulse since otherwise the amplifier |3| would have to supply the full 3,000 volt ampere peak power.

Incorporated in the input circuit of amplifier |3| associated with leads 215 there is a gain or volume control and also a voltage limiting stage to limit .the amplitude of the initial electrical pulse applied by leads 215 to loud speaker 23. The limiter, which may be any of the well known types used in electronic amplifiers, is so adjusted that the voltage of the initial pulse after being limited is comparable to the voltage of the electrical wave train generated by coil |53.

The battle sounds and signals are generated in phonograph pickup 225 and transmitted to the amplifier |3|, wave lters 230, 23| and 232 and loud-speaker 23 in the same manner as described in connection with Fig. 8. The amplifier may contain a gain control to adjust the volume of the loud-speaker sound output.

In the latter embodiment of the invention, the loud-speakers 23 and 250 are disposed in a cab inet 280, which is shown in Fig. 12. and the remainder of the apparatus is housed in cabinet I8. Cabinet 290 is substantially similar in shape to the cabinet I5 shown in Fig. '7, and is supported in a manner similar to that in which cabinet |5 is supported. The cabinet has a substantially horizontal panel 29| for the bottom of the outer portion thereof, which panel has an opening 222 within which the mouth of Speaker 250 is disposed. A diagonally disposed panel 293 encloses the bottom of the midsection of the cabinet, said section having an opening 294 within which the mouth of speaker 23 is disposed. the arrangement being such that the cones of both speakers are directed toward the trainee The cabinet comprises a complete enclosure for the interior thereof, and with proper design of shape 'and volume, it serves to modify and augment the acoustical and mechanical energy delivered by the loud-speakers in a manner such as to efficiently utilize the electrical input and assist in the faithful simulation of the firing phenomena.

In this embodiment of the invention, the contactors may also be arranged to close each circuit upon the occurrence of a voltage peak, and open it upon the occurrence of a current null. The closure may be upon the occurrence of a negative peak as well as a positive peak since I have found that a rarefaction pulse subjectively resembles a condensation pulse providing the pressure of the condensation does not exceed atmospheric pressure. It is an advantage to une a system in which closure occurs on both peaks, because the reversal oi the direction of i'low minimizes pitting of the contacts. Such result may be obtained by employing a synchronous motor having four or more poles and which, therefore, has two or more positions in which the rotor locks in with the rotating field. Each time such a motor is started, the polarity thereof may be reversed with respect to its polarity during its previous operation, that is, the polarity is random with each successive operation and reversals occur frequently.

In this embodiment of the invention, the phase relationship of the energy supplied to each of the two loudspeakers 23 and 250 should be such that the integrated energy of their combined acoustic output is a maximum, that is, that the positive impulses of one do not cancel the negative impulses of the other. If the latter should occur, simulation is noticeably impaired, and the effect may be remedied by reversing the conductors leading to one of the loud-speakers.

In this embodiment, the loud speaker 250 must be large and located in close proximity to the trainee, or to the breech of the gun, in order that a satisfactory air streaming effect be obtained. In practice, a loud-speaker having a diaphragm from 10 to 18 inches in diameter and located within a distance equal to 5 times the diameter of the diaphragm from the operators head or the gun breech has been found to be satisfactory. A position substantially directly over the head of the gunner or the gun breech is also desirable. The need for observing such conditions is made clear .by the following considerations. Air streaming is caused by the mass of air adjacent the diaphragm moving with the diaphragm. This mass creates the effect of increasing the mass of the diaphragm. In the case of a fiat circular piston vibrating in an infinite rigid wall, this apparent increase in the mass on each side of the piston corresponds to the mass of a cylinder of' air having a volume equal to %a3 where a is r the radius of the piston. Therefore, the mass of air which is moved by the diaphragm, is proportional to the third power of the radius of the diaphragm and a great increase in the streaming eilect is obtained by increasing the size of the diaphragm.

At the relatively low frequencies which are involved in the translational air movement present in air streaming the speaker diaphragm behaves substantially as a point source and radiates a wave having a substantially spherical front. In such case, the instantaneous total particle velocity in air is represented by the following equation:

where A is the maximum rate of emission of the air, which is considered to occur at the source or center of the sphere, Z is the length of the radiated wave, r is the distance from the center of the sphere to the point of observation, c is the velocity of sound, and t'is time, all quantities being expressed in a consistent set of units. The first term of the equation represents the radiated sound eld, while the second represents translational particle movement, or the air streaming. The effect of the air flow is, of course, sensible only where there is substantial velocity. The equation shows that the translational velocity .decreases at a rate proportional to the square o! the distance from the source, and that an object must be in close proximity to the source `in order to -be reached `by the air streaming eil'ect.

While the `wave train mechanisms of Fig. `i! and Fig. 11 are shown as having connections to separatemake and break contactors they may,

`ii' desired, bef-connected to the contactors 2H) which serve the'pulse generator when the `mechanism of Fig. 8 is' used and the pulse loudspeaker 2l! when the mechanism of Fig. 11 is The arrangementmay, however, be reversed and the organizationof Fig. 8 may be used with the loud-speaker air streaming generator 250 and the organization of Fig. 11 with the pneumatic pulse generator I 4.

` Whilethe apparatus of this invention vhas been described as being` applicable for combat training, it may also be used with equipment for other purposes, such as target practice equipment and amusement equipment. i

I claim:

l. Apparatus of the class described comprising, in combination. a model gun having nondetonating ymeans for discharging a projectile therefrom and adapted to be operated at will by an operator, a recoil mechanism for said model gun, an air pulse generator arranged to project anair pulse to the position of said operator, separate electromagnetic means for operatingeach of said projectile discharging means, recoil mechanism and air pulse generator, an electromechanical motor.` two coil springs eachat'tached at one end thereof to the output of said electromechanical motor, an electromechanical generator having its input connected totheopposite end of one oi' said coil springs, the other oi' said coil springs being attached to one or more-flexible supports along the length` thereof. said coil springs when at rest being in substantially unstressed condition, a loud-speaker'connected to the output of said electromechanical generator, a source oi.' alternating current `electrical energy. separate electrical supply circuits i'or supplying energy from said source to each of said electromagnetic means and to said electromechanical motor,

means for repeatedly closing andopening said electrical circuits in'synohronism with the energy cycle ofsaid alternating current sourceand in a predetermined time sequence with respect to each other, means for simulating the sound of a moving target, and means for moving a target in' synchronism with said sound.

2. Apparatus of the class described, compris- ,Y

ing, in combination, a model gun having nondetonating means for simulating the projectile discharge of an actual gun, 'a recoil mechanism for said model gun, an air pulse generator, separate electromagnetic means for operating each or said projectile discharge simulating means, recoil mechanism. an air pulse generator, an electromechanical motor, a mechanical transmissionv line composed of alternating compliances and lumped masses connected at one end thereof to the output of 'said motor, an electromechanical generator having its input connected to the other end of said transmission line, a loud-speaker conniected to the outputo! saidgenerator, a source of electrical energy, separate electrical supply circuits for supplying energyfrom said source toeach of said electromagnetic means and to said electromechanical motor, means for repeatedly closing and opening said electrica1` supply circuits in a predetermined time sequence `with respect to each other, means for simulating the sound of a moving target, and means for `moving a target `in synchijonism with said sound. i

3. Apparatus of the class described, comprising, in combination, `a model gun `havingnondetonating operating mechanism, `an air pulse generator, electrical means for operating-said air pulse generator, an electromechanical motor, a mechanical transmission line composed of alternating compliances and lumped masses connected at one end thereof to the output of said 'electromechanical motor, an electromechanical generator having its input connected to the other end of said transmission line, a loud-speaker connected to the output of said generator, a source of electrical energy, separate electrical supply `circuits for supplying. energy from said source to said air pulse generator and said electromechanical motor, and means for closing and opening said electrical `supply circuits in synchronism with said model gun operatingmechanism and in a `predetermined time `sequence with respect to each other.

4. Apparatus of the class described, comprising, in combination, a model gun having non-detonatingoperating mechanism, an air pulse generator,

electrical means for operating said air pulse generator, an electromechanicalmotor, a mechanical transmission line composed of alternating` compliances and lumped masses connected at one end thereof to the output of saidelectromechan-i generator and said electromechanical motor, and means for momentarily energizing said supplycircuit means in synchronism with said model gun operating mechanism. i

5. Apparatus in, accordance with claim 4, in which the air pulse generator comprises means forming an airchamber, ,meansA for supplying air under pressuretofsaid chamber, a generally horn-` `shaped` air radiator `havinga throatl portion thereof in communicationwith said` air chamber, and valve means for establishing andVv disestablishing said communication between said throat portion and said air chamber, said electrical means for operating said air pulse generator being connected said valve means.

6. Apparatus' in accordance with claim `4, in

which the airpulse generator is a loud-speaker.`,

7. Apparatus in accordance with claim `4, `in which the air pulse `generator is a loud-speaker having a diaphragm having a diameter of at least 10 inches, said loud-speaker being located substantially directly above and within a distance equal to Stinnes the diameter of said diaphragm fromthe head oi' the operatorof said gun,

8. Apparatus in accordance with claim 4. in which a single electromechanical transducer constltutes both"the electromechanical motor and the electromechanical generator, said transducer having electrical conductors connected thereto leading from the source of electrical energy and in operative relation to leading to the loud-speaker. whereby said conductors serve as both the electrical input and the electrical output of said transducer and said transmission line sets up a train of mechanical vibrations in said transducer in response to each mechanical impulse resulting from the transducing of an electrical impulse impressed upon the input of said transducer.

9. In apparatus of the class described, means for simulating the air streaming, sound arnd echoes incident to an explosion detonation, cornprising, in combination, an air pulse generator, electrical means for actuating said air pulse generator, an electromechanical transducer having electrical terminals and a mechanically vibratory element, two coil springs of diierent length each attached at one end thereof to the mechanically vibratory element of said transducer, ilexible supporting members for the longer of said springs along the length thereof, spaced apart lumped masses attached to the shorter of said springs along the length thereof, said` springs, when at rest, being in substantially unstressed condition, a loud-speaker connected to the electrical terminals of said transducer. a source of electric energy, electrical supply circuits leading separately from said energy source to said air pulse generator actuating means and said electrical terminals of said transducer, and means for closing and opening said supply circuits in predetermined'time sequence with respect to each other.

10, In apparatus of the class described, means for simulating the air streaming, sound and echoes incident to an explosion detonation comprising, in combination, an air pulse generator, electrical means for actuating said air pulse generator, an electromechanical transducer having electrical terminals and a mechanically vibratory element, two coil-spring members each attached at one end thereof to the mechanically vibratory element of said transducer, flexible supporting members for one of said spring members along the length thereof, lumped masses attached to the second of said spring members at spaced apart points along the length of said second spring member, a loud-speaker connected to the electrical terminals of said transducer, means for momentarily electrically energizing in predetermined time sequence said air pulse generator actuating means and the electrical terminals of said transducer.

11. In apparatus of the class described, means for simulatingan explosion detonation sound and the echoes thereof comprising, in combination, an electromechanical transducer having electrical terminals and a mechanically vibratory element, means for momentarily electrically energizing said electrical terminals, a mechanical transmission line comprising alternating compliance members and lumped masses, said transmission line being attached at one end thereof to said mechanically vibratory element, and a loud-speaker electrically connected to said electrical terminals.

12. In apparatus of the class described, means for simulating an explosion detonation sound and the echoes thereof, comprising, in combination, an electromechanical motor, means for momentarily electrically energizing said motor, two mechanical transmission lines comprising compliance members, said transmission lines having different natural frequencies of vibration and each being attached separately at an end thereof to the vibratory element of said electromechanical motor, an electromechanical generator having its input attached to one of said transmission lines at the end thereof remote from said electromechanical motor, and a loud-speaker connected to the output of said electromechanical generator.

13. In apparatus of the class described, means for simulating the air streaming, sound and echoes incident to an explosion detonation, comprising, in combination, a loud-speaker, a high pass illter network connected to the input of said loud-speaker, a source of alternating current electrical energy, an electromechanical transducer having electrical terminals and a mechani cally vibratory element, means for momentarily and in predetermined time sequence connecting said energy source to said lter network and the electrical terminals of said electromechanical transducer, `a mechanical transmission line comprising a compliance member connected at an end thereof to the mechanically vibratory element of said transducer, and a second loudspeaker connected to the electrical terminals of said transducer.

14. In apparatus of the class described, means for simulating the air streaming, sound and echoes incident to an explosion detonation, comprising, in combination, a loud-speaker, a source of electrical energy, an electromechanical motor, means for momentarily and in predetermined time sequence connecting said energy source to said loud-speaker and said electromechanical motor, a mechanical transmission line comprising a compliance member connected at one end thereof to the output of said electromechanical motor, and a second loud-speaker having its input connected to the other end of said transmission line.

15. In apparatus of the class described, the combination of separate electrical energy respon sive means for simulating respectively the different phenomena of air streaming, initial sound and echoes incident to an explosion detonation, an alternating current source of electrical energy, a separate electrical supply circuit reading from said energy source to the means for simulating each of said phenomena, separate means for closing and opening each of said supply circuits, a synchronous motor for actuating said circuil; closing and opening means in predetermined time sequence, and a supply circuit leading from said alternating current energy source to said motor. y

16. In apparatus of the class described, means for creating an air blast similar to the air streaming incident to an explosion detonation comprising, in combination, a loud speaker, an input. circuit for said loud speaker, means for impressing a momentary electrical impulse upon said input circuit, and means in said input circuit for increasing the steepness of the wave front of said electrical impulse.

17. Apparatus of the classdescribed, comprising, in combination, a model gun having a trigger adapted to be moved to the operative position thereof, separate electrical energy responsive means for respectively discharging a projectile from said model gun and simulating each of the phenomena of recoil, air streaming, initial sound and echoes incident to the tiring of an actual gun, a source of electrical energy, separate supply circuits leading respectively from said energy source to said projectile discharging means and the means for simulating each cf said phenomena, means for closing and opening said supply circuits in predetermined time sequence with respect to each other, said supply circuit closing and opening means being actuated by movement of said trigger to the operative position thereof. 18. In apparatus of the class described, the

`combination of a model gun having a trigger adapted to be moved to the operative position thereof, separate electrical energy responsive means for simulating respectively the different phenomena of initial sound and of echoes incldent to the firing of an actual gun, a source of electrical energy, separate supply circuits leading respectively from said energy source to different ones of said simulating means, means for closing and opening said supply circuits in predetermined time sequence with respect to each other, said supply circuit closing and opening means being actuated by movement of said trigger to the operative position thereof.

19. In apparatus of the class described, the combination of separate electrical energy responsive means for simulating the different phenomena of initial sound and echoes incident to an explosion detonation, a source of electrical energy, separate electrical supply circuits leading respectively from said energy source to each of said effect simulating means, and means for closing and opening each of said supply circuits in predetermined time sequence with respect to each other.

20. .Apparatus of the class described, comprising, in combination, a model gun having a trigger adapted to be moved to the operative position` thereof, means for simulating the different phenomena of air streaming, initialv sound and echoes incident to the firing of an actual gun and causing said simulations to occur in predetermined time sequence with respect to each other, and means for actuating said simulating means upon movement of said trigger to the operative position thereof.

21. Apparatus of the class described, compris,- ing, in combination, a model gun having a trigger adapted to be moved to the operative position thereof. means for moving a target simulating a sound producing object, means for simulating the sound of said object, non-detonating means for simulating the different phenomena of air streaming, initial sound and echoes incident to the firing of an actual gun and causing said simu lations to occur in predetermined time sequence with respect to each other, and means for actuating said last mentioned simulating means upon movement of said trigger to the operativeposition thereof.

22. In combination, means for simulating the operating mechanism of an actual firearm, said means being adapted to be moved to the operative position thereof, and non-detcnating means responsive to said movement to the operative position for producing a shock wave substantially simulating the shock wave produced when an actual firearm is discharged.

23. In combination, a target, means for moving said target, means for simulating the operating mechanism of an actual firearm, said means being adapted to be moved to the operative position thereof, and non-detonating means responsive to said movement to the operative position for producing a shock wave substantiallyl simulating the shock wave produced when an actual firearm is discharged.

24. In combination, means for simulating the operating mechanism of an actual firearm, said `means being adapted to be moved to the operative position thereof, and non-detonating means responsive to said movement to the operative position for producing a shock wave and an echo wave train substantially simulating the shock wave and echo wave train produced when an actual firearm is discharged.

25. In combination, means for simulating the operating mechanism of an actual firearm, said means being adapted to be moved to the operative position-thereof, and non-detonating means responsive to said movement to the operative position for producing an air streaming substantially simulating the air streaming which is produced when an actual firearm is discharged.

26. In combination, means for simulating the operating mechanism of an actual firearm, said means being adapted to be moved to the operative position thereof, and non-detonating means responsive to said movement to the operative position for producing an impulse wave train and an echo wave train substantially simulating the impulse wave train and echo wave train produced when an actual firearm is discharged.

27. In combination, means for simulating the operating mechanism of an actual firearm, said means being adapted to be moved to the operative position thereof, and non-detonating means responsive to said movement to the operative position for producing an acoustic shock impulse and echo wave train substantially simulating the acoustic shock impulse and echo wave train produced when an actual firearm is discharged. Y

28, Apparatus of the class described, comprislng, in combination, a simulated flrearm, a target, said firearm being mounted for movement in alignment with said target, said simulated firearm having means for simulating the operating mechanism of an actual firearm, said means being adapted to be moved to the operative position thereof, and non-detonating means responsive to the movement of said last mentioned means to the operative position thereof for producing a shock wave substantially simulating the shock wave produced when an actual firearm is discharged. o

29. Apparatus of the class described, comprising, in combination, a simulated firearm, a target, said firearm being mounted for movement in alignment with said target, said simulated firearm having means for simulating the voperation of an actual firearm, said means being adapted to be moved to the operative position thereof, and non-detonating means responsive to the movement of said last mentioned means to the operative position thereof for producing a shock wave and an echo wave train in time sequence substantially simulating the shock wave and echo wave train produced when an actual rearm is discharged.

30. `In combination, means for simulating the operating mechanism of an actual firearm, said means being adapted to be moved to the operative position thereof, a source of electrical .en-

ergy, an electroacoustical transducer, means responsive to the movement of said simulating means to the operative position thereof for supplying a sudden pulse of electrical energy from said source to said transducer, and means for controlling the dissipation of energy in said transducer in such manner that the output thereof substantially simulates the related impulse wave train which normally follows the initial shock impulse produced by the discharge 31. In combination. means for simulating the operating mechanism of an actual firearm, said means being adapted to be moved to the operative position thereof, a source of electrical energy, an electroacoustical transducer, means responsive to the movement of said simulating means to the operative position thereof for supplying a sudden pulse of electrical energy from said source to said transducer, and means for receiving pulsating energy from said transducer, storing and returning said energy to said transducer in such manner that the output of said transducer substantially simulates the related impulse wave train which normally follows the initial shock impulse produced by the discharge of an actual firearm.

32. In apparatus of the class described, the combination of a source of electrical energy, an electroacoustical network including a speaker, means for supplying a pulse of electrical energy from said source to said electroacoustical network to simulate acoustical blasting, said network having relatively low energy dissipation characteristics and having a time constant greater than that of said speaker alone to dissipate energy to simulate acoustical booming whereby acoustical blasting and booming is produced by said speaker in time sequence and substantially simulating the acoustical blasting and booming produced when an actual firearm is discharged.

33. In apparatus of the class described, the combination of a source of electrical energy. an electro-acoustical network including a speaker, means for supplying a pulse of electrical energy from said source to said electroacoustical network to simulate acoustical blasting, said network having relatively low energy dissipation characteristics and having a time constant greater thanthat of the speaker alone to dissipate energy to simulate acoustical booming, means `including said network for delaying the application of some of the energy of said pulse to said speaker to simulate echoes of blasting and booming whereby acoustical blasting and booming and echoes thereof are provided by said speaker in time sequence and substantially simulating the acoustical blasting, booming and echoes `produced when an actual firearm is discharged.

34. In `apparatus of the class described, the combination of an electroacoustical network including a speaker adapted for simulating the acoustical blast attendant upon the discharge of a firearm, a source of electrical energy, means for transferring a pulse of said energy to said network over a relatively short time interval, said network having energy storing means associated therewith and arranged to supply energy to said speakerlo'ver a relatively long period of time whereby said speaker radiates acoustical energy for a substantially longer period of time than it receives said pulse of electrical energy from said soluce.

35. The apparatus as claimed in claim 34 in which said energy transferring means includes a switch and means for closing said switch at predetermined times and for a predetermined time interval at each closure thereof.

36. The apparatus as claimed in claim 34 in which said energy transferring means includes a switch and means for closing said switch periodically and for a predetermined time interval at each closure thereof.

37. In apparatus of the class described,- the combination of an electroacoustical network arranged for simulating the acoustical blasting attendant upon the discharge of a iirearm, a source of electrical energy, means for transferring a pulse of said energy to said network over a relatively short time interval, said network having energystoring means of relatively large effect and energy dissipating means of relatively small effect whereby said pulse of electrical energy is converted into acoustical energy as a decaying acoustical wave train.

38. In apparatus of the class described, the combination of an electroacoustical network including a speaker adapted for simulating the blasting attendant upon the discharge of a firearm, a source of electrical energy, means for transferring a pulse of said energy to said network over a relatively short time interval, a second network including an interconnected electricalmechanical system, means for transferring electrical energy from said source to said electrical-mechanical system in predetermined time sequence with respect to said pulse, means for converting mechanical energy in said system to electrical energy, a second speaker, means for amplifying and applying said last mentioned electrical energy to said second speaker, said first and second mentioned speakers being positioned in close proximity for irradiating the same space with acoustical energy.

39. IIhe apparatus as claimed in claim 38 in which the first speaker is arranged to produce air streaming and an acoustical blast.

40. 'I'he apparatus as claimed in claim 38 in which the first speaker is arranged to produce air streaming and an acoustical blast, and the second speaker is arranged to transform electrical energy delivered thereto into acoustical energy after termination of said acoustical blast and in continuation thereof.

41. The apparatus as claimed in claim 38 in which the electrical-mechanical system is adapted to produce a time delay of at least one fiftieth of a second between the radiation of a blast by the first speaker and radiation of acoustical energy by the second speaker.

42. In apparatus of the class described, the combination of an electroacoustical network including a speaker adapted for simulating the blasting attendant upon the discharge of a firearm, a source of electrical energy, means for transferring a pulse of said energy to said network over a relatively short time interval. a second network including an interconnected electrical-mechanical system, means for transferring electrical energy from said source 'to said electrical-mechanical system in predetermined time sequence with respect to said pulse, means for converting mechanical energy in said system to electrical energy, and means for amplifying and converting said lastmentioned electrical energy into acoustical energy.

43. In apparatus of the class described, the combination of electroacoustical means for pro ducing an initial aerial shock impulse simulating the initial aerial shock impulse produced when an explosive is detonated, a second electro acoustical means for producing an acoustical impulse Wave train simulating the impulse wave train normally following the initial aerial shock impulse produced when an explosion is detonated, and means for synchronizing the oper ation of said `iirst and second mentioned means to produce the components of the shock wave produced when an actual explosive is detonated.

44. In apparatus of the class described, the combination of electroacoustical means for producing a shock wave simulating that produced when an explosive is detonated,'a second electroacoustical means for producing a wave train simulating the echoes of the acoustical components of said actual shock wave, and means for synchronizing the operation of said first and second mentioned means to produce a simulation of the shock wave and echoes produced when an explosive is detonated.

45. In apparatus of the character described, an electromechanical transducer having a me chanical member having energy storing properties, said transducer being arranged to produce movement of said mechanical member when voltage is applied to said transducer, a speaker, a source of electrical energy, common means for supplying energy from said energy source to said speaker and from said transducer to said speaker, said common energy supply means containing a voltage limiter arranged to limit below a predetermined magnitude the voltage applied from said source to said speaker.

46. In apparatus of the character described, an electromechanical transducer including a coil and a magnetic member, said coil being mounted for movement relative to said member for inducing a voltage in said coil upon said relative movement of said coil, means including a voltage source for moving said coil relative to said member, a speaker, means for supplying electrical energy from said coil to said speaker, said supply means containing an amplifier for amplitying the voltage induced in said coil.

47. In apparatus of the character described, in combination, apparatus for simulating a rearm, said apparatus including an operating mechanism adapted to be moved to the operative position thereof, means for producing air streaming, and means responsive to movement of said operating mechanism to the operative position thereof for actuating said air streaming means, said air streaming means being so positioned 'with respect to said operating mechanism that the stream of air produced thereby flows past the position of said operating mechanism.

48. In apparatus of the class described, the combination of a source of alternating current electrical energy of substantially fixed frequency, an electroacoustical network including a speaker and a high pass nlter in the input of said speaker, said lier having a cut-od frequency which is higher than the frequency of said source, means for supplying a pulse oi electrical energy from said source to said electroacoustical network to simulate acoustical blasting, said network having relatively low energy dissipation characteristics having a time constant greater than that of said speaker alone to dissipate energy to simulate acoustical booming whereby acoustical blasting and booming is produced by said speaker in time sequence and substantially simulating the acoustical blasting and booming when an actual firearm is discharged.

49. In combination, means for simulating the operating mechanism of an actual rearm, said means being adapted to be moved to the operative position thereof, and electrical means responsive to said movement to the operative position for producing a shock wave substantially simulating the shock wave produced when an actual ilrearm is discharged.

50. In combination, means for simulating the operating mechanism of an actual firearm, said means being adapted to be moved to the operative position thereof, and electrical means responsive to said movement to the operative position for producing a shock wave and an echo wave train substantially simulating the shock wave and echo wave train produced when an actual firearm is discharged.

51. In combination, means for simulating the operating mechanism of an actual firearm, said means being adapted to be moved to the operative position thereof, and electroacoustical means responsive to said movement to the operative position for producing an initial acoustic impulse substantially simulating the initial acoustic impulse which is produced when an actual iirearm is discharged.

52. In combination, means for simulating the operating mechanism of an actual firearm, said means being adapted to be moved to the operative pition thereof, an electroacoustical means responsive to said movement to the operative position for producing an initial acoustic impulse and impulse wave train substantially simulating the initial acoustic impulse and impulse wave train winch is produced when an actual firearm is discharged.

53. In combination, means for simulating the operating mechanism of an actual irearm, said means being adapted to be moved to the operative position thereof, and eiectroacoustical means responsive to said movement to the operative position for producing an initial shock impulse substantially simulating the initial shock impulse which is produced when an actual ilrearm is discharged.

HUGH S. KNOWLES. 

